(1) Field of the Invention
The present invention relates to a novel process for preparing a fluorine-containing compound having a carboxyl group from a fluorine-containing compound having a sulfonyl group. More particularly, the present invention provides a convenient process in which a sulfonyl group of a fluorine-containing compound is converted to a carboxyl group at a high efficiency.
(2) Description of the Prior Art
Various proposals have heretofore been made on the process for converting a sulfonyl group contained in a fluorine-containing polymer to a carboxyl group. For example, we previously proposed processes in which a sulfonyl group (sulfonic acid group) is converted to a sulfonyl halide group and this sulfonyl halide group is subjected to an oxidizing treatment in the presence of an organic solvent (see Japanese Patent Application Laid-Open Specifications No. 132069/78 and No. 83982/79), the sulfonyl halide group is reacted with a phenol (see Japanese Patent Application Laid-Open Specification No. 20981/79) or the sulfonyl halide group is reacted with an amine (see Japanese Patent Application Laid-Open Specification No. 21478/79). Furthermore, there is known a process in which the sulfonyl halide group is treated with a reducing agent such as hydriodic acid (see Japanese Patent Application Laid-Open Specification No. 24177/77). These known processes, however, involve a number of steps, and they are disadvantageous from the economical viewpoint and in view of the process equipment.